Summary: In the mid-1980s we carried out a prospective study of early pregnancy in which we enrolled 221 health women who were planning to become pregnant. These women collected daily urine specimens for up to six months. We've assayed these specimens to describe the hormonal events of the menstrual cycle and early pregnancy. 155 women became clinically pregnant during the study, while 44 had pregnancies that ended so early that the pregnancies were detectable only by assay of urinary human chorionic gonadotropin. This unique study has been called a landmark, and continues to provide a rich resource for the description of the earliest stages of pregnancy. (More than 30,000 urine samples are still being stored.) We've published more than 40 papers from this study over the past two decades, some of which have led to new understanding of the fundamental processes of conception and early pregnancy.[unreadable] In addition, we have continued to make use of large population registries in order to pursue basic questions on pregnancy and maternal and infant health. We have worked especially closely with Norwegian colleagues in the analysis of the Norwegian Medical Birth Registry. [unreadable] [unreadable] Last year's progress.[unreadable] [unreadable] As the obesity epidemic continues to spread in the US and other countries, the effects of obesity on reproduction become an issue of increasing public health importance. An earlier report from NIEHS had suggested that male obesity may reduce the couple's fecundability (the capacity to conceive, measured as a couple's average probability of conceiving in a given menstrual cycle). We used recent data from the Norway Birth Cohort to further test this hypothesis, and found that men who are obese have a substantially decreased risk of conceiving, independent of frequency of intercourse or other recognized factors. This observation raises new questions about endocrine effects of obesity.[unreadable] [unreadable] We are interested in the factors that trigger the delivery of a baby. Despite intense interest in the causes of preterm delivery and delivery more generally, there is remarkably little information about the processes that initiate labor and delivery. We used generational data from the Norwegian Medical Birth Registry to explore genetic components of this phenomenon, assessing the extent to which the length of pregnancy of the mother and the father are related to the length of pregnancy of their offspring. We fould associations between father and offspring (as well as with mother and offspring), suggesting that genetic factors transmitted through the fetus contribute to the onset of labor. This evidence for contributions of the fetus to onset of labor may suggest new biological pathways for those who are exploring the mechanisms of labor and delivery more directly.